The National Transportation Safety Board said the plane’s “feathering” system, which typically requires two steps, initiated on its own.

On Friday, shortly after being dropped from a cargo aircraft over the Mojave desert, Virgin Galactic’s SpaceShip Two exploded at a height of 45,000 feet, seriously injuring pilot Pete Siebold, who managed to eject from the spacecraft before it disintegrated, and killing co-pilot Michael Alsbury. It casts an ominous fog over Virgin founder Richard Branson’s budding space tourism efforts, where customers are invited to pay $250,000 per seat for the chance to flown to the edge of space and back. Branson was hoping to start commercial flights as early as next spring.

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As for what caused the crash, the National Transportation Safety Board (NTSB) said in an announcement Sunday that, per its ongoing investigation, the plane may have splintered apart when its “feathering” system–in which the tail rotates upward to create drag–deployed early and without warning. The system typically requires two separate steps to activate, reports the Guardian, and is intended to help SpaceShipTwo decelerate. Here’s what feathering looks like, per a video taken in May 2011:

The NTSB says the co-pilot reportedly activated the first step, but the second step occurred “without being commanded,” causing the plane to curl before it had a chance to hit Mach 1.4, or 1.4 times the speed of sound. At this point, it is unclear if the deployment was a mechanical failure. A conclusive investigation could take up to a year.

Earlier reports suggested that the crash may have been related to a combustion problem with a newly redesigned rocket motor, but that might no longer be the case; the aircraft’s fuel tanks and engine were discovered intact.

It puts Virgin Galactic’s space plans in a quandary. More than 700 hundred customers, including musician Justin Bieber, actress Angelina Jolie, and astrophysicist Stephen Hawking, have already reserved seats for the first batch of commercial space flights. (One additional customer reportedly signed up after Friday’s crash to show support for the program.)

“We do understand the risks involved, and we are not going to push on blindly,” said Branson in a statement. “To do so would be an insult to all those affected by this tragedy. We’re going to learn from what went wrong, discover how we can improve safety and performance, and then move forward together.”

“Of course, anyone who ever wants a refund will get a refund,” he added.

About the author

Chris is a staff writer at Fast Company, where he covers business and tech. He has also written for The Week, TIME, Men's Journal, The Atlantic, and more.